Downstream Synchronization State Machine for Optical Line Terminal (OLT)-Configurable Bit Interleaving in High-Speed Passive Optical Networks (PONs)

This is a continuation of U.S. patent application Ser. No. 18/162,457, filed on Jan. 31, 2023, entitled “Downstream Synchronization State Machine for Optical Line Terminal (OLT)-Configurable Bit Interleaving in High-Speed Passive Optical Networks (PONs),” which is a continuation of International Patent Application No. PCT/US2021/046524, filed on Aug. 18, 2021, entitled “Downstream Synchronization State Machine for Optical Line Terminal (OLT)-Configurable Bit Interleaving in High-Speed Passive Optical Networks (PONs),” which claims the benefit of U.S. Provisional Patent Application No. 63/091,657 filed Oct. 14, 2020, by Xiang Liu, et al., and entitled “Downstream Synchronization State Machine for Optical Line Terminal (OLT)-Configurable Bit Interleaving in High-Speed Passive Optical Networks (PONs).” All of the aforementioned applications are hereby incorporated by reference in their entireties.

The present disclosure is generally related to the field of optical networks and, in particular, to optional interleaving in optical networks.

Optical networks are networks that use optical signals to carry data. Light sources such as lasers generate optical signals. Modulators modulate the optical signals with data to generate modulated optical signals. Various optical network components transmit, propagate, amplify, receive, and process the modulated optical signals. Optical networks may employ multiplexing to achieve high bandwidths. Optical networks implement data centers, metropolitan networks, PONs, long-haul transmission systems, and other applications.

The disclosed aspects/embodiments provide techniques permitting an Optical Network Unit (ONU) receiving a downstream signal to detect whether an Optical Line Terminal (OLT) has implemented non-interleaving or has implemented bit-interleaving when formulating the downstream signal. The ONU searches for a physical synchronization sequence (PSync) pattern in all possible alignments for all possible OLT bit-interleaving modes within the downstream signal. The ONU performs this pattern search to determine whether the OLT was using non-interleaving or a certain mode of bit-interleaving to encode the downstream signal sent to the ONU.

A first aspect relates to a method implemented by an optical network unit (ONU) in a passive optical network (PON), comprising: receiving an encoded downstream (DS) signal from an optical line terminal (OLT); searching for a physical synchronization sequence (PSync) pattern in all possible alignments for all possible OLT bit-interleaving modes within the downstream signal; and transitioning to a pre-synchronization state once the PSync pattern has been found.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the all possible OLT bit-interleaving modes comprises a non-interleaving mode and a mx bit-interleaving mode in which m adjacent forward error correction (FEC) codewords are interleaved on a bit-by-bit basis.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that m is set to 4.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the FEC is based on low density parity check (LDPC).

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the FEC codeword length is 17,280 bits.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that during the searching, the ONU switches between a non-deinterleaving mode and a mx bit-deinterleaving mode every N consecutive failures to find the PSync pattern, wherein N is at least the length of a physical layer (PHY) frame and wherein the mx bit-deinterleaving mode comprises deinterleaving the m adjacent FEC codewords on a bit-by-bit basis.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that m is set to 4.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the FEC is based on low density parity check (LDPC).

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the FEC codeword length is 17,280 bits.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the length of the PHY frame comprises 6,220,800 bits.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the ONU is in a Hunt state while performing the searching.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the ONU is unsynchronized while in the Hunt state.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the all possible alignments comprise one or more of bit alignments and byte alignments.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the downstream signal comprises one or more physical layer (PHY) frames.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that searching for the PSync pattern includes error-tolerant pattern matching.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that searching for the PSync pattern comprises verifying a superframe counter (SFC) hybrid error control (HEC).

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the PSync pattern has been found when the PSync pattern with up to a maximum number of bit errors (K) has been detected.

A second aspect relates to an optical network unit (ONU) in a passive optical network (PON), comprising: a memory configured to store instructions; and one or more processors coupled to the memory, the one or more processors configured to execute the instructions to cause the ONU to: receive an encoded downstream (DS) signal from an optical line terminal (OLT); search for a physical synchronization sequence (PSync) pattern in all possible alignments for all possible OLT bit-interleaving modes within the downstream signal; and transition to a pre-synchronization state once the PSync pattern has been found.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the all possible OLT bit-interleaving modes comprises a non-interleaving mode and a mx bit-interleaving mode in which m adjacent forward error correction (FEC) codewords are interleaved on a bit-by-bit basis.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that m is set to 4.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that during the search, the ONU is configured to switch between a non-deinterleaving mode and a 4× bit-deinterleaving mode every N consecutive failures to find the PSync pattern, wherein N is at least the length of a physical layer (PHY) frame and wherein the mx bit- deinterleaving mode comprises deinterleaving the m adjacent FEC codewords on a bit-by-bit basis.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the length of the PHY frame comprises 6,220,800 bits.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the ONU is in a Hunt state while performing the search.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the ONU is unsynchronized while in the Hunt state.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the all possible alignments comprise one or more of bit alignments and byte alignments.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the downstream signal comprises one or more physical layer (PHY) frames.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the search for the PSync pattern includes error-tolerant pattern matching.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the search for the PSync pattern comprises verifying a superframe counter (SFC) hybrid error control (HEC).

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the PSync pattern has been found when the PSync pattern with up to a maximum number of bit errors (K) has been detected.

A third aspect relates to a passive optical network (PON), comprising: an optical line terminal (OLT) configured to transmit an encoded downstream (DS) signal; and an optical network unit (ONU) in communication with the OLT, wherein the ONU is configured to perform the method in any of the disclosed embodiments.

A fourth aspect relates to an optical network unit (ONU) means in a passive optical network (PON), comprising: memory means configured to store instructions; and processing means configured to execute the instructions to cause the ONU means to: receive an encoded downstream (DS) signal from an optical line terminal (OLT); search for a physical synchronization sequence (PSync) pattern in all possible alignments for all possible OLT bit-interleaving modes within the downstream signal; and transition to a pre-synchronization state once the PSync pattern has been found.

For the purpose of clarity, any one of the foregoing embodiments may be combined with any one or more of the other foregoing embodiments to create a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

In a high-speed PON (HSP) such as the 50-gigabit-capable passive optical network (50G-PON), bit-interleaving over multiple adjacent forward error correction (FEC) codewords is an optional feature for downstream signal (a.k.a., downstream transmission). Therefore, an optical line terminal (OLT) has the option of switching between using non-interleaving and using bit-interleaving when formulating downstream signal. Unfortunately, there is currently no way for the optical network unit (ONU) receiving the downstream signal to detect whether the OLT will implement non-interleaving or bit-interleaving when formulating the downstream transmission.

Disclosed herein are techniques permitting the ONU receiving the downstream signal to detect whether the OLT has implemented non-interleaving, or has implemented a certain mode of bit-interleaving when formulating the downstream signal. The ONU searches for a physical synchronization sequence (PSync) pattern in all possible alignments for all possible OLT bit-interleaving modes within the downstream signal. The ONU performs this pattern search to determine whether the OLT was using non-interleaving or a certain mode of bit-interleaving to encode the downstream signal sent to the ONU.

is a schematic diagram of a PON. The PONcomprises an OLT, ONUs, and an ODNthat couples the OLTto the ONUs. The PONis a communications network that may not require active components to distribute data between the OLTand the ONUs. Instead, the PONmay use passive optical components in the ODNto distribute the data.

The OLTcommunicates with another network and with the ONUs. For instance, the OLTtransfers data from the other network to the ONUs, and transfers data from the ONUsto the other network. The OLTis typically located at a central location such as a central office (CO), but it may also be located at other suitable locations.

The ODNis a data distribution network that comprises optical fiber cables, couplers, splitters, distributors, and other suitable components. The components include passive optical components that do not require power to distribute data between the OLTand the ONUs. The ODNmay extend from the OLTto the ONUsin a configuration as shown, or may be configured in any other suitable point-to-multipoint (P2MP) configuration.

The ONUscommunicate with the OLTand with customers. For instance, the ONUstransfer data from the OLTto the customers and transfer data from the customers to the OLT. ONUsand optical network terminals (ONTs) are similar, and the terms may be used interchangeably. The ONUsare typically located at distributed locations such as customer premises, but they may also be located at other suitable locations.

is a schematic diagramillustrating data path functions including optional interleaving and deinterleaving within downstream (DS) signals. As shown in the upper sequence, datais obtained by an OLT (e.g., the OLT). The OLT utilizes, for example, a low density parity check (LDPC) encodingto encode the datafor FEC. The OLT then scramblesthe encoded data. The OLT may or may not perform interleavingon the encoded data. That is, the interleavingis optional. When performed, it is desirable that the interleaving be performed over consecutive LDPC codewords on a bit-by-bit basis, which is herein abbreviated as mx bit-interleaving. Preferably, 4× bit-interleaving is performed. For example, with the 4× bit-interleaving, every four adjacent LPDC codewords with a codeword length of 17280 bits, represented as [AA. . . ABB. . . BCC. . . CDD. . . D], are interleaved to [AABBCCDD. . . ABCD]. The function of the interleavingis to mitigate the performance degradation of FEC in the presence of correlated errors, which may be introduced due to channel equalization. After the interleaving, the downstream signal is transmitted over a transmission channel(a.k.a., the PON physical channel), so the common transmission convergence layer (ComTC) is minimally impacted. Thereafter, the encoded data is transmitted, by the OLT, over the transmission channeltoward one or more ONUs (e.g., ONUs).

When received, the ONU may or may not perform deinterleavingon the encoded data received from the OLT over the transmission channel, depending on whether interleaving is detected in the encoded data. That is, the de-interleavingmust be performed by the ONUif interleaving was performed by the OLT. When performed, the deinterleavingmay be performed over consecutive LDPC codewords on a bit-by-bit basis, which is herein abbreviated as mx bit-deinterleaving. Preferably, 4× bit-deinterleaving is performed. For example, with the 4× bit-deinterleaving, every four interleaved LPDC codewords with a codeword length of 17280 bits, represented as [AABBCCDD. . . ABCD], are de-interleaved to [AA. . . ABB. . . BCC. . . CDD. . . D], which is the original data sequence right before the interleaving. The ONU descramblesthe encoded data. After the encoded data has been descrambled, the ONU then decodes the encoded data using, for example, LDPC decoding.

In an embodiment, the descrambling is performed by a descrambler within the ONU that uses the scrambling polynomial x+x+1. In an embodiment, the descrambler uses a variable starting bit sequence derived from the superframe counter (SFC). In an embodiment, the SFC is obtained after FEC decoding. In an embodiment, a variable starting sequence is [1 1 1 1 1 1 1 SFC].

Notably, the order of operations performed in the upper sequencemay be changed, as shown in the lower sequence. In the lower sequence, datais obtained by an OLT (e.g., the OLT). The OLT scramblesthe data. The OLT then utilizes, for example, LDPC encodingto encode the scrambled data. The OLT may or may not perform interleavingon the encoded data. That is, the interleavingis optional. Thereafter, the encoded data is transmitted, by the OLT, over a transmission channeltoward one or more ONUs (e.g., ONUs).

When received, the ONU may or may not perform deinterleavingon the encoded data received from the OLT over the transmission channel. That is, the deinterleavingis optional. The ONU decodes the encoded data using, for example, LDPC decoding. The ONU then descramblesthe LDPC decoded data.

When 4× bit-interleaving is utilized in the upper sequenceor the lower sequence, a physical synchronization sequence (PSync) of SSS. . . SS, where S represents bits of the PSync, becomes SxxxSxxxSxxx . . . SxxxSxxx, where x represents bits of data interleaved into the PSync. Because the PSync pattern is changed when the optional 4× bit-interleaving is used, the downstream state machine needs to be modified to accommodate the optional 4× bit-interleaving.